Welcome to Ask a Biogeek, a column where you ask UC Berkeley researcher Terry Johnson any question you want - no matter how weird. Reader Matthew asks:

This is an odd question, but is there anything we're certain isn't coming? Most of my friends are all starry-eyed optimistic sci-fi readers, and they continually bombard me with what will be the "future of the human species" . . . from "meat vats" for growing cruelty free meat to clone armies. Anyway, is there anything that is solidly stymied at this point? Any futurist direction we know is blocked?

"Blocked" is perhaps too rigorous a standard, but there are certainly some futures far less likely than others. I can't prove a negative, but perhaps I can convince you that a few common science fiction or futurist tropes are, shall we say, favored poorly by probability.Grey Goo Eats the Planet Self-replicating molecular machines run amok, proving so capable of turning other molecules into copies of themselves that Earth's ecosystem is completely taken over by an amorphous mass of presumably-grey nanotechnology. Futurists and science fiction writers have imagined nanotech ecophages that originate on our planet, through nanoweapons research or mutations in beneficial nanotechnology, along with alien nanotech - whether star-faring remnants of some other species' lab accident or a deliberate attempt at genocide. These vivid visions of a nanotechnological apocalypse caught on with the public, despite much evidence to the contrary. Nanotechnologist Eric Drexler originally coined the term "grey goo", and now rather wishes he'd hadn't. No one is working on self-assembling nanomachines that even hint at the abilities a true ecophage would require, and concerns over the catastrophic (though enormously unlikely) grey goo scenario turn attention away to more pedestrian health concerns, like toxicology. Oh noes! Considering biology, I'm fairly confident that if grey goo were possible, we'd be living in it. Single-celled organisms have been doing chemical experimentation for billions of years via mutation and natural selection, and if there was a magic, self-catalyzing molecule out there, I expect they'd have found it. It wouldn't be for lack of trying - protein enzymes perform chemistry all the time, and RNA can both catalyze reactions and store genetic information. I don't discount the possibility that killer grey goo molecules could merely be difficult or impossible to synthesize using the amino acids, nucleotides, and raw materials that life on earth manipulate and depend upon - but life has been pretty clever about applying those resources so far, and the closest nature has come to a self-replicating nanomachine would probably be a prion. Though disease-causing prions are notoriously difficult to destroy, they have yet to convert the Earth's biomass into mad cows. An amazingly successful organism - not a single molecule replicating itself, but a more complex collection of molecules, like a cell - could potentially lead us into a Green Goo Ragnarök. On Earth, however, it would find an already-existing ecosystem full of the survivors of a molecular arms race that began in the primordial soup. A newbie might be able to find a niche or even flourish, but to displace all other life on Earth is asking a bit much - though the results of a partial takeover and significant shift in Earth's ecosystem could still be disastrous to humanity. A Meal in a Pill Your body requires a certain amount of carbohydrates, protein, and fats. Add in the necessary fiber, and an "average" human being needs at in the ballpark of 250 grams of food. Assuming a density of around 1.0 gram per cubic centimeter, my back of the envelope calculation suggests that a pill taken three times daily would be a few inches in diameter. Fry: "I cant swallow that." Professor Hubert Farnsworth: "Well, then, good news! It's a suppository." Even neglecting essential vitamins and minerals, that's not easy to swallow. The military, long interested in convenient, non-perishable foodstuffs, is considering a transdermal nutrient delivery system instead. A Universal Translator The prevalence of universal translation devices in science fiction has more to do with avoidance of subtitles than scientific plausibility. It's difficult enough to wrap up the "A" plot in a 42-minute television episode if every line requires manual translation by non-native speakers. Mysteriously English-speaking aliens may strain credulity, but without them, crackling dialogue is a challenge. Linguistics posits a basic universal grammar shared by all known languages, though in typical anthrocentrism this grammar is universal only to humans. Alien grammar needn't share much of anything with ours, and the language itself could be composed of sounds, smells, flashing lights, posture, magnetic fields, spurts of superheated plasma, or some complex combination of these or other phenomena. Real-time translation of known alien languages would be complicated enough - the device would have to detect every possible phenomena that an alien could use to communicate with on top of the translation task. Translation of new languages would require enough exposure to learn the vocabulary. Star Trek's universal translator posits universal concepts shared by all intelligent beings - a pretty big "if" - and associates brainwaves with these concepts. Imagine a pocket-sized functional MRI machine that sees the patterns associated with a certain universal concept and translates it into your language. Sounds great - but it assumes a central nervous system suspiciously similar to our own. That's reasonable when your galaxy is filled with beings who resemble you (with bumpier foreheads) - for us, probably not so much. Do you have questions you've always wanted to ask a biogeek? You can email me.